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Evidence-based Medicine Resource Center
Fact Sheet

WHY FINDING "EVIDENCE" IN MEDLINE CAN BE FRUSTRATING: TOP COMPLAINTS AND QUESTIONS

by The Librarians' Working Group

1. MEDLINE is comprehensive. It includes citations to many articles, letters, editorials that do not necessarily provide valid, reliable "evidence" for application to clinical practice. Learning techniques for effectively identifying articles for evidence-based practice is time-consuming. The learning curve can be daunting and not feasible for pace of patient care.

2. There are many interfaces to MEDLINE available to the practicing physician, and more are being added each day. The database and its contents may be the same from one interface to another, but there are major, and minor quirks in using specific interfaces. The CD ROM version you learned to search in medical school may be quite different than the World Wide Web version in use in your hospital. Translating what you already know about searching into the language of a new system interface can be a frustrating experience.

3. Librarians tell physician-searchers that one of MEDLINE's strengths is its indexing - provision of subject headings and subheadings to assist searchers in locating articles. "Use the thesaurus," they say. "It can be more efficient than free text searching. Even a novice can locate headings this way". But the indexing seems to be confusing and inconsistent. Headings and subheadings can change from year to year. And if you are using PubMed (which includes PreMedline), your search may eliminate going really recent articles simply because of the lack of indexing. The effective search strategy will accommodate retrieval quirks for indexed and non-indexed articles.

4. Methodology headings are increasing. While this is potentially a boon for the EBM searcher, the headings often seem redundant. It is difficult to know which to use. Some subject headings, such as "clinical trials," are similar, or even identical, to publication types. It seems necessary to use publication types, as well as subject headings, to get the best retrieval - a cumbersome, confusing technique. It often seems necessary to supplement subject heading searching with free text searching to get optimum results. It seems it is necessary to spend an inordinate amount of time and energy in learning and working with and around MEDLINE's idiosyncrasies. Trying to outwit an imperfect system is time-consuming and not cost-effective.

5. Do all searches have to be either "sensitive" or "specific"? This is the search terminology used in most of the EBM searching literature. Yet, when trying to do a "sensitive" search, one can end up with hundreds of irrelevant citations, needing to browse through them. Is there any happy medium between a search that's too broad and one that is too restrictive?

6. It is difficult to locate systematic reviews in MEDLINE. Sometimes they are indexed to the subject headings, "review literature", or "meta-analysis". Sometimes they are indexed to the publication types, "review" and "meta- analysis". But including these methodological filters, a search strategy can yield narrative reviews, as well as systematic reviews. Free text seems to be the best way to go here. Why is there no effective search term for systematic reviews?

7. MEDLINE doesn't cover everything. That is both the good news and the bad news. You could possibly miss an article simply because it is not indexed in MEDLINE.

8. Yes, MEDLINE is difficult to learn. To search for evidence for clinical practice, it seems less frustrating and more cost-effective to go immediately to value-added databases, such as the "Cochrane Library", or the "ACP Library". They are easier to search and are quality filtered. But there are problems with these time-saving databases. They cover far fewer journals than does MEDLINE, and there is an even greater time lag between the publication of the article, and its appearance in these databases, than there is with MEDLINE.

9. While exploding a term is the most effective way of getting everything on a topic, it can also get you a some things that are completely off-topic. It can be difficult to know exactly when to avoid term explosion, and when to use it to enhance retrieval. Only the searcher can determine what is relevant.

10. Depending upon which MEDLINE interface you are using, it can be unclear as to when the database was last updated. A CD ROM version of MEDLINE, for example, may be updated much less frequently than an online or World Wide Web version of the database. It can be difficult to know if you are retrieving the most recent studies available.

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Updated: 11/2/98
Patricia E. Gallagher